As discussed in more detail below, many diagnostic tests depend on the visual examination and appraisal of a color which is developed in a sample of biological material by treatment of the sample with reagents that generate color in positive correlation with the amount of an analytes, i.e. a particular compound to be assayed (e.g. cholesterol) or specific molecular markers present in the sample indicative of a pathological condition, such as cancer.
Tests which require the visual examination and appraisal of the color changes are convenient and often adequate as a preliminary, subjective assessment for the presence of a target compound or a disease marker, but they are essentially non-quantitative.
I have found, surprisingly, that measurement of the hue angle and/or chroma, as well as related color characteristics, by reflective spectrophotometry, affords at least semi-quantitative measurement of the result of assays. From such measurement of one or more defined characteristics of the color of an assay sample derive much valuable information concerning the presence or absence of progressive diseases such as cancer, as well as their stage of development.
Color-Based Test for Cancer
From U.S. Pat. No. 5,162,202, it is known to screen rectal mucous from human patients for detection of colorectal cancer and cancers of the large intestine. The mucous is collected on a membrane filter. A cellulose membrane filter is pre-prepared by impregnation with a solution of the enzyme galactose oxidase in a phosphate buffer, and then lyophilized. At the time of use, the cellulose membrane filter is moistened and then contacted with the membrane filter carrying the mucous sample, for 1-2 hours. Then the mucous bearing membrane filter is washed and reacted with basic fuchsin for 15 minutes, washed and dried. De-colorization of the fuchsin indicates the presence of carbohydrate markers of a cancerous or pre-cancerous condition in the mucous. Such a test is lengthy and tedious to perform, and does not have a high degree of sensitivity, so that it may give false negatives.
An improved rectal mucous test is disclosed in U.S. Pat. No. 5,348,860 Shamsuddin, issued Sep. 20, 1994. In this procedure, the mucous sample is collected and immobilized on a membrane filter, and is treated with galactose oxidase to effect oxidation of any vicinal galactose moieties in the sample to vicinal aldehyde moieties. These are visualized with Schiff's Reagent. This is a more rapid procedure. Samples which test negative by this procedure can be further oxidized with periodic acid and then visualized with Schiff's Reagent, so as to reduce the chances of obtaining false negative results.
A continuing problem with known mucous tests is that the staining results need to be visually examined and appraised. Whilst such examinations are adequate as a preliminary, subjective assessment for the presence of absence of cancer markers, they are qualitative only. They do not give reliable quantitative information about the amounts and concentrations of markers which have been found, and which could give indications of the state of progression of the cancer condition, if present. Moreover, the medium on which the samples are developed, normally a cellulose membrane, such as filter paper, may itself contain compounds capable of participating in the color development reactions. This can give a “background” which complicates the interpretation of the test results, and reduces its sensitivity. This requires a trained individual skilled in the interpretation of the test result.
Color-Based Assay of Cholesterol Levels
The association of high serum cholesterol levels in patients with propensity to develop atherosclerosis and consequent increased incidence of coronary heart attack, stroke and PVD is firmly established, so that frequent monitoring of patient's cholesterol levels is desirable. More commonly, cholesterol level is determined from extracted blood samples. Many other diagnostic tests are commonly performed also on extracted blood samples, but most of these need only be conducted at longer intervals than cholesterol tests. The invasive nature of the blood collection procedure for cholesterol analysis discourages many patients from undergoing cholesterol monitoring as frequently as is advisable. Accordingly, there is a need for a non-invasive cholesterol test.
It is estimated that the skin contains about 11% of the body's total cholesterol, resulting largely from epidermal steroidogenesis and cholesterol diffusion from blood vessels. It has been postulated that the level of skin cholesterol may more accurately reflect the extent of atherosclerosis than the amount of serum cholesterol.
Nikitin, Y P, Gordenko, I. A., Dolgov, A. V. and Filimonova, T. A., “Cholesterol Content in the Skin and its Correlation with Lipid Quotient in the Serum in Normals and in Patients with Ischemic Cardiac Disease”, Cardiology 1987 II, No. 10, page 48-51, and others, have demonstrated that there is a close correlation between cholesterol content in the arterial wall and cholesterol content in the skin of a patient. This suggests a possibility of developing skin tests to determine a patient's cholesterol level. The method described by Nikitin et al., however, involves removing and analyzing skin samples in vitro, a method which is impractical in a clinical setting.
U.S. Pat. Nos. 5,489,510 and 5,587,295 Lopukhin et al., describe a non-invasive diagnostic test which is performed on the surface of the patient's skin, and which indicates skin cholesterol levels. In the test described in these patents, reagents are provided in the form of affino-enzymatic compounds which are bi-functional in their nature. The bifunctional compound A-B includes a binding agent A which is capable of discriminately forming stable complexes with cholesterol of the skin in order to give the whole bi-functional compound an affinity to cholesterol (for example digitonin); and a visualizing agent B, for example an enzyme such as peroxidase, which permits detection of the bi-functional compounds bound to skin cholesterol. In the practice of this test, a complex of a binding agent A and a visualizing agent B, optionally in combination with a bridging agent C to enhance the sensitivity of the test, i.e. a bi-functional conjugate A-C-B, may be placed on the skin of the palm of the patient. Bridging agent C is suitably a high molecular weight polyfunctional compound such as a polysaccharide or a protein, and serves to space the visualizing agent from the binding agent to minimize steric hindrance of the cholesterol-binding agent reaction. After a suitable incubation period to ensure binding of the complex to the cholesterol of the skin, the area is fully rinsed with clean water to remove unbound reagents. Then the binding area is treated with indicating agent D, to react with visualizing agent B so as to develop color. The greater the cholesterol level, the greater the degree of binding of the bi-functional compound to the skin, and the greater the degree of color development.
A cholesterol test based on the aforementioned patents of Lopukhin et al. has been developed commercially and put into commercial practice. It involves the provision of a kit comprising reagents and a color chart or reader. Most of the reagents are contained in a vial, which the user applies to the test area, on the palm of the hand, after removing the protective covers. After incubation, the user applies indicating agent and visually assesses the degree of color change which occurs, alongside the color chart or using the reader.
One disadvantage of such a test is the requirement for visual assessment of the color changes. Whilst it is convenient that the test can be carried out by un-skilled personnel, such as the patient, the visual assessment of the resultant color change is subjective and essentially non-quantitative. It can give a valuable indication of cholesterol levels and hence potential problems, but not the type of quantitative measurements which a prescribing physician commonly prefers. The assessment is easily influenced by the nature and color of the background, namely the skin.
It is the general object of the present invention to provide a novel method for determining and measuring the result of a color-based biochemical or immunological assay which does not rely on subjective visual assessment. It is a further and more specific object to provide a method for the quantifiable measurement of the amount of a target compound in a sample of biological material which has been subjected to a biochemical or immunological assay that generates a color in positive correlation with the amount of said target compound.
It is also an object of the present invention to provide a novel test of body secretions, liquid and semi-solid, and a kit for use therein, useful in cancer diagnosis.
It is a further and more specific object of the present invention to provide a novel test of rectal mucous and other secretions, liquid and semi-solid, including stool, and mixtures thereof, and a kit for use therein, which overcomes or at least significantly reduces one or more of the above disadvantages. In the following description, the term “colon-contacting semi-solids” is used to denote mucus, stool and other liquids or semi-solids obtained from the rectum or colon of a patient, and mixtures thereof, which provide the analyzable material for use in the process of the present invention.
It is also an object of the present invention to provide a novel diagnostic, non-invasive test for cholesterol.
It is a further and more specific object to provide such a test for cholesterol which is capable of producing at least semi-quantitative results.